致命错误应用程序停止工作

Question

首先，我是初学者。

我正在遵循本指南：

https://www.youtube.com/watch?v=T7Z4GVFaT4A

然后当我完成对此视频的编程。我收到了这个错误：

FATAL EXCEPTION: main
Process: com.spotcrime.loginregister, PID: 5951
java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
  at com.spotcrime.loginregister.RegisterActivity$1.onClick(RegisterActivity.java:40)
  at android.view.View.performClick(View.java:4780)
  at android.view.View$PerformClick.run(View.java:19866)
  at android.os.Handler.handleCallback(Handler.java:739)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at android.os.Looper.loop(Looper.java:135)
  at android.app.ActivityThread.main(ActivityThread.java:5254)
  at java.lang.reflect.Method.invoke(Native Method)
  at java.lang.reflect.Method.invoke(Method.java:372)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

现在这是我的两个活动的代码。

RegisterRequest.java

     package com.spotcrime.loginregister;

     import com.android.volley.Response;
     import com.android.volley.toolbox.StringRequest;

     import java.util.HashMap;
     import java.util.Map;

 public class RegisterRequest extends StringRequest {

//allow us to make request to php file from server and get reponse as a string

//specify where our url of php file is

private static final String REGISTER_REQUEST_URL = "http://spotcrime.net23.net/Register.php";
private Map<String, String> params;

//create constructor for class (first method that runs when instance of this class created

public RegisterRequest(String name, String username, int age, String password, Response.Listener<String> listener){
    //pass data to volley
    super(Method.POST,REGISTER_REQUEST_URL, listener, null);
    params = new HashMap<>();
    params.put("name", name);
    params.put("username", username);
    params.put("password", password);
    params.put("age", age + ""); //age + "" converts from int to string
}

@Override
public Map<String, String> getParams() {
    return params;
}
  }

RegisterActivity.java

public class RegisterActivity扩展了AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_register);

    //final variable because it wont be assign to anything else after this
    //find ageregister cask it to edittext
    final EditText etAge = (EditText) findViewById(R.id.etAgeRegister);
    final EditText etName = (EditText) findViewById(R.id.etNameRegister);
    final EditText etUserName = (EditText) findViewById(R.id.etUsernameLogin);
    final EditText etPassword = (EditText) findViewById(R.id.etPasswordRegister);
    final Button bRegister = (Button) findViewById(R.id.bRegisterRegister);

    bRegister.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            final String name=etName.getText().toString();// text to string
            final String username=etUserName.getText().toString();// text to string
            final int age=Integer.parseInt(etAge.getText().toString());// text to string
            final String password=etPassword.getText().toString();// text to string

            //need to create response listener

            Response.Listener<String> responseListener = new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    try {
                        JSONObject jsonResponse = new JSONObject(response);
                        boolean success = jsonResponse.getBoolean("success");
                        if (success) {
                            Intent intent = new Intent(RegisterActivity.this, LoginActivity.class);
                            RegisterActivity.this.startActivity(intent);
                        } else {
                            AlertDialog.Builder builder = new AlertDialog.Builder(RegisterActivity.this);
                            builder.setMessage("Register Failed")
                                    .setNegativeButton("Retry", null)
                                    .create()
                                    .show();
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            };

            RegisterRequest registerRequest = new RegisterRequest(name, username, age, password, responseListener);
            RequestQueue queue = Volley.newRequestQueue(RegisterActivity.this);
            queue.add(registerRequest);
        }
    });
}
}

我不知道是什么问题。我在互联网上研究过。当我构建它时，我没有错误。我假设它指向空值但不确定。